1. Field of the Invention
The present invention relates to a camera having a focus adjusting function and a lens apparatus adapted to the focus adjusting function.
2. Description of Related Art
Conventionally, a number of cameras with focus adjusting functions and lens apparatuses adapted to the focus adjusting functions have been commercialized. These products automatically focus on an object by measuring the distance to the object or detecting a defocus amount of an image-taking optical system with a focus detecting unit and driving a focusing lens.
In focusing lens control in the above-mentioned products, in order to improve focusing accuracy, high stop position accuracy is required. To obtain high stop position accuracy, it is necessary to stop the focusing lens at a low speed. Therefore, it is generally difficult to complete focusing in a short period.
Various methods for increasing the speed of driving the focusing lens have been achieved to solve this problem. For example, in an image-taking lens the focal length of which is variable, such as a zoom lens, by using the focal depth that becomes deep at the wide-angle side and becomes shallow at the telephoto side, the focusing lens is driven at a high speed at the wide-angle side and driven at a low speed at the telephoto side.
However, in this case, since the final stop position accuracy of the focusing lens is uniformly set to the highest stop accuracy required at the telephoto side, the period of stopping the focusing lens cannot be sufficiently reduced even at the wide-angle side at which high-speed driving is allowed.
Furthermore, the focal depth is also changed by setting of the aperture diameter of a diaphragm, the stop position accuracy of the focusing lens can be eased when the aperture diameter of the diaphragm is small. A method for controlling the stop position of a focusing lens by detecting the state of a diaphragm has been proposed in Japanese Laid-Open No. H07-77648. The purpose of this proposal is power savings, which does not lead to an increase in the speed of automatic focusing.